The invention relates to a multiplex wiring system.
Multiplex wiring systems for automobiles are known for reducing the large number of wires required to link automobile accessories with the appropriate accessory switch and to link automobile displays with the appropriate automobile sensor. In general terms, each accessory switch and each sensor are coupled via appropriate transmitters to a data bus line. Similarly, each accessory and each display or other receivers of sensor information such as, for example, control processors are coupled via appropriate receivers to the same bus line.
Multiplex wiring systems are known wherein a transmitting node serially transmits data on a data bus to which a plurality of receiving nodes are connected. The serial stream of transmitted data typically includes: a start-of-message, an address for a particular receiving node, and instruction data. Each receiving node detects the start-of-message for actuating the appropriate receiving circuitry. Only the designated receiving node recognizes its own address and then acts upon the instruction data following the address data. An example of such a system is disclosed in U.S. Pat. No. 3,651,454 issued to Venema et al.
A problem with these systems has been that a failure in the data bus may disable a large portion of the automobile's electronic circuitry. An additional problem is that the failure may be difficult to diagnose and correct. A further problem is that noise on the data bus may be misinterpreted as data resulting in a temporary and unpredictable failure of the autombile's electronic system.
U.S. Pat. No. 3,891,965 discloses a different type of multiplex system wherein the address information is sent over a multitude of parallel address lines which are physically separated from the data buses. Complementary address codes are assigned to each sender/receiver set so that, in the event of a failure on one address line, the receiving set may still recognize its own address. Two parallel data buses, carrying identical data, are also disclosed. The data bus lines are tied together by isolation diodes. In the event that one of the data buses becomes shorted to the automobile ground, the isolation diode will isolate that particular bus from the receiving node. This system, however, does not appear to teach any method for recognizing, or protecting against, other forms of failure in the data bus such as a short to power or an open circuit condition.
The need still remains for a multiplex wiring system which will continue to operate during a wide range of failures in the data bus such as when the data bus is shorted to power, shorted to ground, or open circuited. A need also remains for providing comprehensive information about the type of faults on the data bus. Further, a need remains for rejecting noise on the data bus which may be misinterpreted as data.